In a wireless local area network (WLAN) a number of wireless access points (APs) form the wireless infrastructure, and wireless hosts communicate with each other via the wireless APs. The wireless hosts may be stationary or may roam around. Such a system is similar to any cellular network system.
A requirement for antennas at a wireless access point, or in a base station of a cellular network, is that the radiation must be omni-directional in the azimuth plane, in order to give an equal chance of access to all mobiles around it. There is a continuing desire for higher gain, omni-directional antennas, in particular for wireless APs, so as to extend the cell size in a cellular network and/or increase communication reliability of cells. However, such improvements need to be achieved whilst minimizing the cost, size and technical complexity of the antennas.
A good example of an omni-directional antenna is the well-known half wavelength dipole antenna which has a so-called "donut" shaped radiation pattern providing good omni-directional coverage. Such well-known half-wavelength dipole antenna's have a signal gain of 2 dBi, which can be insufficient for the desired large cell size/good communication reliability required or wireless AP antennas. A gain of 5 dBi can provide substantial improvements in omni-directional coverage.
The 2 dBi gain of a half-wavelength dipole antenna can be increased by "squashing" the "donut" radiation pattern across its vertical cross-section, thus changing it from the "donut" shape of a well-known half-wavelength dipole antenna to a "squashed donut", being flatter and larger in the azimuth plane.
Theoretically, such a pattern modification can be obtained, for example, by means of a couple of ordinary half-wavelength dipoles vertically stacked on top of each other to form a collinear array and fed in phase. However, the implementation of such an antenna can be troublesome primarily due to difficulties in arranging the feeding for the array elements in such a way as to avoid disturbing the radiation pattern. Known solutions to the problem of providing a feeding network in the collinear array add to the cost, size, or technical complexity of the antenna, which is undesirable.
It is therefore an object of the present invention to provide a feeding arrangement suitable for use in a collinear array antenna which can be implemented in a collinear array without unduly increasing the technical complexity thereof, which minimizes interference with the radiation pattern of the antenna, and which does not unduly add to the physical size of the antenna.